The purpose of this work is to study the cells that participate in the effector arm of the immune response. The current emphasis is on chemotaxis, which is a mechanism by which cells can be attracted to inflammatory sites, delayed hypersensitivity reactions and growing tumors. The project includes chemistry of lymphocyte derived chemotactic factors, identification of substances that modulate chomotactic and phagocytic responses and definition and separation of functional subpopulations of leukocyes.